In recent years, environmental issues such as global warming believed to be caused by an increase in carbon dioxide have become serious, and therefore measures against such environmental issues have been taken on a global basis. Above all, solar cells utilizing the energy of sunlight have been actively researched and developed as environmentally-friendly clean energy sources. As such solar cells, monocrystal silicon solar cells, polycrystal silicon solar cells, amorphous silicon solar cells, and compound-semiconductor solar cells have already been practically used, but these solar cells have problems such as high production cost etc. For this reason, dye-sensitized solar cells have received attention as solar cells that are environmentally friendly and can be produced at lower cost, and research and development of such dye-sensitized solar cells have been promoted.
An example of the general structure of a dye-sensitized solar cell is shown in FIG. 11. As shown in FIG. 11, a general dye-sensitized solar cell 100 has a structure comprising: abase material for dye-sensitized solar cell 110 having a base material 111 and a first electrode layer 112 laminated on the base material 111, and a counter electrode base material 120 that functions as an electrode, and a porous layer 102 containing dye sensitizer-supported fine particles of a metal oxide semiconductor and an electrolyte layer 101 provided inside a sealant 103 and interposed between the base material for dye-sensitized solar cell 110 and the counter electrode base material 120. Therefore, the dye sensitizer adsorbed to the surface of the metal oxide semiconductor fine particles contained in the porous layer 102 is excited by receiving sunlight from the base material 111 side, and excited electrons are transferred to the first electrode layer and then transferred to the counter electrode base material through an external circuit. Then, the electrons are returned to the ground state of the dye sensitizer by a redox couple so that electricity is generated.
Such a dye-sensitized solar cell conventionally uses a glass substrate as a base material. However, in recent years, there has been a demand for flexible dye-sensitized solar cells, and therefore the use of a flexible substrate as a base material has been contemplated. However, when a flexible base material is used, there is a problem that the base material is bent and therefore an internal short circuit is caused by electrical contact between the first electrode layer and the counter electrode base material.
In order to solve such a problem, for example, Patent Literatures 1 and 2 disclose that a separator, such as an insulating porous film, is provided between a counter electrode layer and a power-generating layer composed of a porous layer and an electrolyte layer to prevent a short circuit. Further, Patent Literature 3 discloses that a spacer is provided on a counter electrode layer to prevent a short circuit. All the electrolytes used in Patent Literatures 1 to 3 are liquid.
However, a dye-sensitized solar cell having an electrolyte layer using such a liquid electrolyte has the problem of high production cost because the electrolyte layer usually needs to be sealed with an expensive sealant having high resistance to iodine contained in the electrolyte, and further has a problem that, even when the electrolyte layer is sealed with such a sealant, there is a possibility that liquid leakage from the electrolyte layer occurs. Further, as described above, since the production of such a dye-sensitized solar cell having an electrolyte layer using a liquid electrolyte requires sealing with a sealant, alignment between a base material for dye-sensitized solar cell and a counter electrode base material for bonding requires high accuracy. Further, in such a dye-sensitized solar cell, the sealant needs to be provided outside a region where a porous layer is provided, and therefore adjustment of the formation position of each of the members of the dye-sensitized solar cell also requires high accuracy. Therefore, such a dye-sensitized solar cell has a problem that its production process is complicated.
In order to solve such problems, a dye-sensitized solar cell having a solid electrolyte layer using a solid electrolyte instead of such a liquid electrolyte as described above has been studied. Such a dye-sensitized solar cell having a solid electrolyte layer uses a solid electrolyte having no fluidity, and therefore can be produced at low cost without sealing the solid electrolyte layer with such an expensive sealant as described above. The use of such a solid electrolyte also makes it possible to solve the problem of liquid leakage from an electrolyte layer. Further, as described above, since it is not necessary to perform sealing with a sealant, alignment between a base material for dye-sensitized solar cell and a counter electrode base material for bonding and adjustment of the formation position of each of the members of the dye-sensitized solar cell do not require high accuracy. This eliminates the above-described complications associated with the production of a dye-sensitized solar cell using a liquid electrolyte and makes it easy to produce a dye-sensitized solar cell.
Such a dye-sensitized solar cell using a solid electrolyte layer is also required to use a flexible base material.
When such a dye-sensitized solar cell using a solid electrolyte layer uses a flexible base material, a base material for dye-sensitized solar cell and a counter electrode base material can be separated from each other by a laminated body composed of the solid electrolyte layer and a porous layer, which is advantageous in that the necessity to use a member such as the above-described separator or spacer can be eliminated.
However, such a dye-sensitized solar cell using a solid electrolyte layer has a problem that there is a possibility that an internal short circuit occurs due to contact between the base material for dye-sensitized solar cell and the counter electrode base material in a region surrounding the porous layer. In order to solve such a problem, for example as shown in FIG. 12, a dye-sensitized solar cell in which a base material for dye-sensitized solar cell 1 and a counter electrode base material 2 are not opposed to each other around a porous layer 4 has also been studied. However, in this case, there is a problem that alignment between the base material for dye-sensitized solar cell and the counter electrode base material for bonding requires high accuracy, which complicates the production process of the dye-sensitized solar cell. It is to be noted that a detailed description of FIG. 12 will be made later.